There’s a very good reason to update your iPhone or iPad to the latest version of iOS–9.3.1. It fixes a bug that bricked the device when the clock was set back to January 1, 1970, writes security researcher Brian Krebs in a blog post.

The bug was originally discovered by another researcher, Zack Straley, back in February. Here’s Straley demonstrating it in a video.

The bug didn’t get much attention because how many users would just randomly decide to set their device clock back to 1970? It gets scarier. Another pair of researchers–Patrick Kelley and Matt Harrigan–recently demonstrated that a hacker could set up a predatory Wi-Fi network that would set the time back on i-devices that auto-connected to it.